Lag fuse



Nov. 9, 1954 G. F. LAING HA1. 2,694,124

LAG FUSE Filed April 16, 1952 2 Sheeis-Sheet 1 g Z0 Z8 3 14 40 42 mmg/f w United States Patent Ofiice 2,694,124 Patented Nov. 9, 1954 LAG FUSE Gordon F. Laing, Delavan, Wis, and Gustav Rensner,

Chicago, Ill., assignors to Economy Fuse and Mannfacturing Co., Chicago, 111., a corporation of Illinois Application April 16, 1952, Serial No. 282,601

11 Claims. (Cl. 200-123) This invention relates to lag fuses, and especially lag fuses of the dual element type which are adapted for use in low amperage circuits.

The present invention embodies certain principles of construction and operation which have been presented in the prior United States Laing Patent No. 2,543,245, issued on February 27, 1951, and United States Laing Patent No. 2,613,297, issued on October 7, 1952.

The present invention utilizes the plunger type retractible elements which are adapted to conduct both heat and electricity when in closed circuit position, and are capable of being moved to open circuit position once their mass has attained a temperature equal to the melting point of the eutectic solder used to maintain the parts together.

These elements are usually massive in form in order to provide for the accumulation of a predetermined amount of heat before attaining the temperature required to open the circuit.

In the plunger type fuse construction shown in the United States Laing Patent No. 2,613,297, issued on October 7, 1952, the parts are maintained in closed circuit position against the bias of a spring internally of the casing, which is mounted essentially in surrounding relation to such parts, and which upon melting of the solder causes the parts to separate to break the circuit.

In United States Laing Patent No. 2,543,245, issued on February 27, 1951, the open circuit is attained again by means of a spring, but in this instance it is mounted in the end of the casing and acts upon one of the connecting fuse links to cause the latter to withdraw from a fusible central element which acts both as a heat reservoir and as a fusible release to permit the spring to retract the fuse link to open circuit position. This construction requires that the fuse link be attached to an internal movable cap, against which the outer end of the spring expands, which, in turn, must be connected to the end wall of the fuse link chamber by a piece of flexible conductor so as positively to connect electrically the outer terminal cap and the fuse link without reliance upon sliding contacts for the transmission of the electrical current.

Obviously, this is a complication in the number of parts and in the assembly of the device, which it is the intention of the present construction to avoid.

It is, therefore, the primary object of this invention to simplify the constructions similar to those discussed above, and to combine an end spring actuator with a plunger type heat and electrical conductor, instead of with a fusible element, so as to circumvent the difficulties and disadvantages heretofore encountered in such arrangements.

Referring now more particularly to the drawings:

Figure l is a plan view of one embodiment of the present invention shown with certain parts in section;

Figure 2 is a mid-sectional elevational view of the device shown in Figure 1, taken at substantially 90 degrees from the latter view shown with the parts in closed circuit position;

Figure 3 is a view corresponding to Figure 2, shown with the parts in open circuit position; and

Figures 4, 5 and 6 are views corresponding, respectively, to Figures 1, 2 and 3 of a modified form of the invention.

In Figures 1 to 3 there is illustrated a fiber casing 15 of insulating characteristic having metallic terminal caps 12' and 14 pressed thereon, substantially to enclose the same. Disposed within the casing so as to divide it into three chambers is a pair of diaphragms 16 and 18 which may be in the form of fiber washers. Massive metallic heat and electrical conductor elements 24 and 26 are arranged in the central chamber of the casing against the diaphragms therein in spaced relation to each other.

The diaphragms are apertured so that a fuse link 20 extends from the terminal 12 through the diaphragm 16 into electrical and heat conducting relation with the element 24, and the fuse link 22 extends from the terminal 14 through the diaphragm 18 correspondingly in heat and electrical conductive relation with the element 26 except that in this instance the element 22 is off-center for reasons to be presently discussed. The side chambers across which the fuse links extend are preferably filled with quenching powder 23.

A central plunger 28 is slidably mounted centrally of the element 26 and is fastened in connecting relation between the elements 24 and 26 by eutectic solder 30, which has a predetermined melting point to free the plunger 28 when the heat resident in the central ele ments exceeds the temperature at which the solder melts.

The fuse link 20 at its outer end is inserted through an aperture in the cap 12 and ends in a depression exteriorly of the cap, which forms a repository for solder 32, into which the link 20 extends so as to become permanently secured thereto. The opposite link 22 extends through the cap 14 and in this instance is turned over as at 34 so as to lie against the outer face thereof, to which it is permanently and stationarily soldered.

A tension rod 36, which is united to the plunger 28 through the center of the diaphragm 18, extends through the center of the terminal cap 14 and has secured to its outer end a stop or inner cap 38. The coil-spring 40 is confined between the caps 14 and 38 so that when the plunger 28 is soldered in closed circuit position as shown in Figure 2, the spring 40 exerts an expansive force which tends to separate the caps 14 and 38, as well as the central conductor element 24 and the plunger 28.

The links 20 and 22, which may be made of brass or zinc, or any other well-known material for this purpose, are designed to blow upon sudden excessive overloads, but are intended to pass moderate overloads which, while insuificient to destroy the links themselves, are nevertheless sufficient over periods of time gradually to increase the resident heat of the parts, particularly those in the central compartment, until the eutectic solder is melted, whereupon the spring is free to withdraw the plunger 28 from electrical connection with the element 24 into the open circuit position, as shown in Figure 3.

Fuses of this kind are designed to have an overall terminal cap 42, which is in electrical engagement with the inner cap 14. The inner and outer caps are dimensioned so that the combined thickness and overall diameter of the two caps is substantially equal to that of the cap 12 on the opposite end of the casing. A window 44 permits visual observation of the position of the cap 38 within to determine whether the fuse has been moved to open circuit or not.

In operation, electric current enters the fuse by the metallic terminal elements 12 and 1442, and is conducted through fuse links 20 and 22, respectively, and

r through the massive conductor elements 24, 28 and 26,

when the parts are in closed circuit position. Upon short circuit, one or both of the fuse links 20, 22, will blow out to open the circuit. Upon less severe overloads. the soft solder 30 between the massive conductors 24 and 26 and the plunger 28 insures maintenance of the circuit through the fuse until sufficient heat has been stored in the massive elements to melt the solder, whereupon the spring 40 is enabled to draw the plunger 28 through the tension rod 36 to open circuit position against the massive element 26, as appears in Figure 3.

The same overall construction applies in connection with Figures 4, 5 and 6 as that just described, except for the elements in the central compartment defined by the diaphragms 16 and 18. Therefore, only these 0 latter will be described.

Instead of the parts 24, 26 and 28, there are in this modification substituted therefor, elements 54, 56 and 58, respectively. The block 54 has a recessed portion 60, which is dimensioned to accommodate the movable part 58, which in this instance is of the same size and shape and is complementary to the block 56, in relation to which it slides. Eutectic solder is disposed at the interface of the parts 54 and 58 to hold them in closed circuit position, as shown in Figure 5. When the solder is melted, the spring 40 causes the slide 58 to retract into the position shown in Figure 6, so as to establish open circuit. Otherwise, the construction and arrangement of parts are as have already been described in connection with the preceding figures.

It will be noted that in the embodiments of the present invention herein disclosed, the need for the flexible conductor between the inner stationary cap 14 and the stop or inner movable cap 38 has been eliminated by making the fuse link mounting independent of the tension rod 36 by which the plunger is moved. Therefore, it is possible permanently to connect the link 22 or its counterparts with the element 26 or 56, or other equivalent, and the terminal cap 14. Since all of these parts are stationary and are in fixed electrical union with the outer overall cap 42, it is not necessary to include the movable cap 38 in circuit, as is the case in Laing Patent No. 2,543,245 mentioned above, and the flexible conductor is not required for this purpose, as is necessary when the functions of the link and the tension rod are combined in the one element. Also, because the tension rod 0ccupies the axial position centrally of the casing, the link must be placed off-center as was mentioned in the fore part of this description.

We claim:

1. Lag fuse construction comprising an insulator casing, terminals closing said casing, partitions spaced within said casing to divide it into at least three chambers, two massive heat and electric conductor elements disposed in an intermediate chamber in spaced relation, a slide element of good heat and electrical conductivity having a bearing upon one of said conductor elements extending between both of the latter when in closed circuit position, fuse links connecting said massive conductor elements respectively to their adjacent terminals, and a tension rod connected to said slide element extended through one of said terminals having a stop secured to its outer end, and a compression spring positioned between said stop and adjacent terminal.

2. The invention of claim 1, said slide element being maintained in closed circuit position between said conductor elements by a fusible material against the bias of said spring.

3. The invention of claim 2, said fusible material being a eutectic solder of predetermined melting point.

4. The invention of claim 1, in which said conductor elements and said slide element are arranged essentially coaxially with each other and with said casing, said bearing of said slide element upon one of said conductor elements being a telescopic bearing.

5. The invention of claim 1, in which said conductor elements have superficial slide bearings on which said slide element is adapted to move from bridging relation between the conductor elements to open circuit position upon one of them.

6. A lag fuse comprising an insulator casing, terminal caps closing the ends of said casing, diaphragms disposed interiorly of the casing to divide it into central and end chambers, relatively massive heat and electric conductor metallic elements arranged in said central chamber in spaced relation to each other, one of said elements being made in two relatively movable parts that are adapted to be expanded to bridge the space between the elements in the central chamber and to be retracted to open said space; links extending from said central chamber through said end chambers and being connected, respectively, to one of said elements and the adjacent terminal cap, a spring for retracting the movable parts of the one of said elements, said spring being mounted at an end of said casing, and a pull-rod connecting the force of said spring with the movable parts in the central chamber thereof.

7. The invention of claim 6, in which said spring is enclosed in an outer terminal cap cover, said covering being permanently secured to the adjacent inner terminal caph cover closing said casing in electrical contact there- W1 8. The invention of claim 7, a window in said outer terminal cap cover through which the position of said spring and associated parts can be observed.

9. The invention of claim 7, in which the links extending from both of the elements in the central chamber to their respective terminal caps are permanently secured thereto in fixed relation therewith for the transmission of electrical and mechanical energy expressed as heat therebetween.

10. The invention of claim 6, in which said relatively movable parts in said central chamber are held in expanded position to bridge the space between said elements by a eutectic solder of predetermined melting point.

11. The invention of claim 6, in which said end chambers are filled with quenching powder.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 825,879 Deisenhofer July 10, 1906 2,410,370 Thielers et a1 Oct. 29, 1946 2,543,245 Laing Feb. 27, 1951 

